You could say that about almost every adjective. Your logic seems to imply that no one should ever dare hold an opinion or make an assertion.
For "intuitive" on the other hand, even the meaning of the word is not clear. I think that it means "aligns well with one's previous experiences". That, however, means that it is idiotic to say that "this UI is intuitive", just as it is idiotic to say that "this line is orthogonal"---you have to specify _to_what_ that line is orthogonal, and _to_whom_ the UI is intuitive.